Composite substrate for light emitting diodes

ABSTRACT

A low-cost device for packaging LED dies provides superior reflectivity and thermal conductivity without covering entire surfaces of an LED luminaire with an expensive reflective aluminum substrate. The LED packaging device includes a highly reflective substrate disposed in a hole in a printed circuit board. The substrate has a reflectivity greater than 97% and includes an insulating layer and a reflective layer disposed above a thicker aluminum layer. An LED die is disposed on the top surface of the substrate. The PCB has a layer of glass fiber in resin and a metal layer. The lower surface of the PCB and the bottom surface of the substrate are substantially coplanar. The metal layer of the PCB is electrically coupled to the LED die only through bond wires. Electronic circuitry is disposed on the upper surface of the PCB and is used to control light emitted from the LED die.

TECHNICAL FIELD

The present invention relates generally to packaging for light-emittingdiodes, and more particularly, to a composite substrate that maintainshigh reflectivity and thermal conductivity at lower cost.

BACKGROUND INFORMATION

A light emitting diode (LED) is a solid state device that convertselectrical energy to light. Light is emitted from active layers ofsemiconductor material sandwiched between oppositely doped layers when avoltage is applied across the doped layers. Multiple LED dies aretypically packages together in an LED array. In one example, an array ofLED dies is mounted onto a heat conducting substrate, and a layer ofsilicone is disposed over the LED dies. When a current is driven throughthe LED dies, the dies emit blue light. Some of the blue light emittedfrom the LED dies is absorbed by phosphor particles embedded in thesilicone and is re-emitted by the phosphor particles as longerwavelength light. The combined light emitted by the LED dies andphosphor particles has a wider band of wavelengths. Some of the emittedlight does not, however, exit the LED package because the light isabsorbed by surfaces of the package. Thus, a first desirable quality ofLED packaging is having highly reflective surfaces that reflect as muchlight as possible from the LED package.

In addition, while emitting light, the LED dies and the phosphorparticles also generate heat. The performance and operational lifetimeof the LED dies is degraded if the operating temperature exceeds athreshold level. Empirical data demonstrates that there is an inverserelationship between the useful life of an LED die and the amount bywhich the average operating temperature exceeds a threshold level, suchas 25 degrees Celsius. In order to remove enough heat from the LED diesso as to keep the LED dies adequately cool, the LED package is typicallyfixed in some way to a heat sink. Thus, a second desirable quality ofLED packaging is effectively dissipating the heat generated by the LEDdies.

And of course low cost is a third desirable quality of LED packaging. Inan attempt to reduce the cost of LED packaging, bare LED dies can beattached directly to a large printed circuit board in a chip-on-board(COB) manner in order to eliminate the manufacturing step of mountingthe dies onto smaller substrates that are themselves attached to theboard. The overall cost can be reduced by transferring the manufacturingsteps of die attaching, wire connecting and encapsulating to the circuitboard assembly stage.

FIG. 1 (prior art) is a cross-sectional view of chip-on-board packaging10 in which light-emitting diode (LED) dies 11-16 are directly mountedonto an aluminum substrate 17 that is covered by a reflective layer 18and an insulating layer 19. Conductive traces 20 are deposited over theinsulating layer 19, and bond wires 21 electrically connect contacts onthe LED dies 11, 16 to the conductive traces 20. Subsequently, silicone22 containing phosphor particles 23 is poured into a dam 24 and hardensforming a conformal covering over the LED dies 11-16. The silicone layer22 also protects the bond wires 25. Although the chip-on-board packaging10 does exhibit the two desired LED packaging qualities of effectiveheat dissipation and high reflectivity, the cost of using the highlyreflective aluminum substrate as an entire surface of the LED luminaireis exceedingly expensive.

A low cost method of packaging LED dies is sought that provides superiorreflectivity and thermal conductivity but yet reduces cost by avoidingcovering entire surfaces of the LED luminaire with expensive highlyreflective layers.

SUMMARY

A low-cost device for packaging LED dies provides superior reflectivityand heat conductivity without covering entire surfaces of a luminairewith expensive, highly reflective substrates. The LED packaging deviceincludes a highly reflective substrate disposed in a hole in a printedcircuit board. The highly reflective substrate has a reflectivitygreater than 97% and includes an insulating layer and a reflective layerdisposed above a thicker aluminum layer. LED dies are mounted directlyto the top surface of the substrate. The printed circuit board has alayer of glass fiber in resin and a metal layer. The lower surface ofthe printed circuit board and the bottom surface of the substrate aresubstantially coplanar. The bottom surface of the substrate is thermallycoupled to the upper surface of a heat sink through a thermal interfacematerial. The metal layer of the printed circuit board is electricallycoupled to the LED dies through bond wires, and no electrical connectionis made to any LED die disposed on the top surface of the substrateexcept through bond wires.

Electronic circuitry is disposed on the upper surface of the printedcircuit board and is used to control light emitted from the LED dies.For example, drive electronics disposed on the upper surface of theprinted circuit board receives a higher voltage and supplies a lowervoltage to the LED dies. The LED packaging device is covered by moldedplastic or by a plastic encapsulant. The drive electronics is disposedbetween the upper surface of the printed circuit board and the insidesurface of the molded plastic cover, or the drive electronics isconformally overmolded with the plastic encapsulant. A seal is createdby a double-sided adhesive sheet that is disposed under the insidesurface of the molded plastic cover and over the upper surface of theprinted circuit board.

In one embodiment, the top surface of the substrate is lower than theupper surface of the printed circuit board, and a layer of siliconecovers the substrate and the LED dies. Particles of phosphor arecontained in the layer of silicone. In another embodiment, the topsurface of the substrate and the upper surface of the printed circuitboard are coplanar. In one embodiment, the highly reflective substrateis a disk that fits in a cylindrical hole in the printed circuit board.The printed circuit board has a lower indentation in the lower surface,and the substrate disk has a lower lip. The thickness of the lower lipof the substrate disk equals the depth of the lower indentation in theprinted circuit board.

Further details and embodiments and techniques are described in thedetailed description below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 (prior art) is a cross-sectional view of chip-on-board packagingwith LED dies directly mounted onto a reflective aluminum substrate.

FIG. 2 is a cross-sectional view of a highly reflective aluminumsubstrate onto which LED dies have been mounted in a chip-on-board (COB)manner.

FIG. 3 is a cross-sectional view of an LED packaging device with LEDdies mounted onto a highly reflective aluminum substrate inserted into ahole in a printed circuit board onto which electronic components aremounted.

FIG. 4 is a perspective view of the LED packaging device of FIG. 3covered by a plastic encapsulant that together with overmoldedelectronic components forms an integrated smart lighting module.

FIG. 5 shows an LED packaging device that includes LED dies mounted ontoa highly reflective aluminum substrate inserted into a hole in a thickerprinted circuit board.

FIG. 6 is a perspective view of an aluminum substrate and a PCBillustrating how small portions of the aluminum substrate are insertedinto holes in the PCB.

FIG. 7 shows the LED packaging device of FIG. 5 used in a low-profile,outdoor lighting module.

FIG. 8 is a different perspective view of the outdoor lighting module ofFIG. 7.

FIG. 9A is a longitudinal cross-sectional view through the LED packagingdevice of FIG. 5 used in the lighting module of FIG. 7.

FIG. 9B is an exploded view of the elements of the LED packaging deviceand lighting module shown in FIG. 9A.

FIG. 10 shows the bottom side of the lighting module of FIG. 7.

FIG. 11 shows the lower surface of a PCB before disks of a reflectivealuminum substrate are inserted into openings in the PCB.

FIG. 12 shows a disk of a reflective aluminum substrate with mounted LEDdies before it is inserted into an opening in a PCB.

FIG. 13 shows the top side of a PCB after disks of an aluminum substratehave been inserted from the bottom into openings in the PCB.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 2 shows a highly reflective aluminum substrate 26 onto which lightemitting diodes (LEDs) 27-32 have been mounted in a chip-on-board (COB)manner. The LED dies 27-32 are placed directly onto the substrate 26 inthe die-bonding process. In one implementation, gold bond wires link theLED dies 27-32 in series, and the ends of the series-connected stringsof LED dies are wire bonded to conductive traces deposited on the topsurface of the aluminum substrate. In one embodiment, the top surface ofthe aluminum substrate is an insulating layer. The aluminum substrate 26itself performs the functions of light reflection and heat dissipation.A luminaire made with the COB aluminum substrate 26 can be placeddirectly on a heat sink without any intervening printed circuit boardlayer. In another embodiment, substrate 26 has a base layer made ofceramic or a metal other than aluminum, such as copper.

Mounting the LED dies 27-32 directly onto an aluminum substrate thatcontacts a heat sink eliminates the manufacturing step of mounting thedies onto small aluminum substrates that are themselves attached toanother substrate from which heat must be dissipated. The manufacturingcost of the COB aluminum substrate 26 is reduced by transferring themanufacturing steps of attaching and wire bonding the dies to thecircuit board assembly stage.

However, highly reflective aluminum substrate 26 is still relativelyexpensive because of the multiple layers used to achieve the highreflectivity. Aluminum substrate 26 achieves a reflectivity exceeding97%. Substrate 26 has a thicker base aluminum layer 33 with a thicknessof 0.5 to 0.8 mm covered by a thinner 75-nm layer 34 of aluminum oxide(Al₂O₃). In some embodiments, the base aluminum layer 33 can be a coinedrolled aluminum that has been mirror-finished at the time of rollingbefore it is silver plated. The aluminum oxide layer 34 is covered by avery thin layer 35 of titanium oxide (TiO₂) that separates a thickerlayer of silver 36 from the aluminum oxide layer 34. The titanium oxidelayer 35 is about one nanometer thick, and the silver layer 36 is about170 nanometers thick. The titanium oxide layer 35 prevents the silver inlayer 36 from migrating down into the base aluminum layer 33. Thereflectivity of aluminum substrate 26 would be reduced if the silver inlayer 36 were to become depleted through absorption into the basealuminum layer 33. The silver layer 36 is covered by a 45-nm insulatinglayer 37 of aluminum oxide, which itself is covered by a 45-nmreflective layer 38 of titanium oxide.

Layers 34 and 37 of aluminum oxide form insulating layers, and layers 36and 38 of titanium oxide form reflective layers. But the silver layer 36forms the primary reflector. Aluminum oxide layer 37 and titanium oxidelayer 38 on top of silver layer 36 protect the silver film againstcorrosion. The optical thicknesses of layers 37-38 are chosen so thatthey do not reduce the reflectivity of silver layer 36. Otherembodiments of aluminum substrate 26 can have more reflective layers toachieve an even higher reflectivity. For example, multiples pairs oflayers with differing refractive indices may be deposited over the basealuminum layer 33 in order to form a distributed Bragg reflector on thealuminum substrate 26. The layers of the Bragg reflector may be placedabove or below other single reflective layers. Each additionalinsulating and reflective layer adds to the cost of the highlyreflective aluminum substrate 26. Thus, the cost can be reduced bycovering only those surfaces of a luminaire with the expensive, highlyreflective substrate 26 that are close to LED dies.

FIG. 3 is a cross-sectional diagram of a low-cost device 39 forpackaging LED dies that provides superior reflectivity and heatconductivity without covering entire surfaces of an LED module with theexpensive highly reflective aluminum substrate 26. The device 39includes the LED dies 27-32, the highly reflective substrate 26 and aprinted circuit board 40. Drive electronics that control and power theLED dies are mounted onto the printed circuit board 40, and aninsulative molded plastic encapsulant 41 encases and encapsulates thePCB 40 and the drive electronics. The drive electronics are electroniccomponents, such as a microcontroller integrated circuit 42 and aswitching DC-to-DC converter 43. In the example of FIG. 3, the switchingDC-to-DC converter 43 is a buck converter. Thus, the drive electronicsof the lighting module can receive a higher voltage and supply a lowervoltage to the LED dies. Each of the electronic components is a packageddevice that is in turn overmolded by the plastic encapsulant 41. The LEDpackaging device 39 together with the overmolded electronic componentsforms an integrated smart lighting module. The lighting module is“smart” because the drive electronics can supply a regulated constantcurrent to the LED dies.

Each of the LED dies includes epitaxial layers of gallium-nitride grownon a sapphire substrate or on a substrate of crystalline silicon. Thegallium-nitride LED dies emit blue light with a wavelength of about 450nanometers when a sufficient drive current is passed through the diodes.In one embodiment, the printed circuit board 40 is a type of FR-4 boardand has a layer 45 of glass fiber in resin, a metal layer 46 and a layer47 of solder mask. The metal layer 46 is typically a copper foil with athickness of less than 0.1 mm. The resin can be bismaleimide-triazine(BT) epoxy resin. In another embodiment, the printed circuit board 40 isa CEM-1 board (Composite Epoxy Material) with laminated paper sandwichedbetween glass fiber and resin and covered by copper foil.

Only small portions of the highly reflective aluminum substrate 26 belowthe LED dies are used in the LED packaging 39. The small portions of theCOB aluminum substrate 26 are inserted into holes in the printed circuitboard 40. The portions of substrate 26 can be circular, square orrectangular. In the embodiment of FIG. 3, the small portion of substrate26 is a circular disk, and the hole in the printed circuit board 40 iscylindrical. After the substrate 26 is inserted into the hole in theprinted circuit board 40, the lower surface 49 of the printed circuitboard 40 and the bottom surface 50 of the substrate 26 are substantiallycoplanar. This allows the LED packaging 39 to establish a good thermalcontact with the planar surface of a heat sink. In the embodiment ofFIG. 3, the top surface 51 of the substrate 26 and the upper surface 52of the printed circuit board 40 are also substantially coplanar.

The substrate 26 includes the insulating layer 37 disposed above thethicker base aluminum layer 33, and the reflective layer 38 disposedabove the insulating layer 37. The LED dies 27-32 are mounted directlyonto the top reflective layer 38. The LED dies 27-32 are electricallyconnected in series by bond wires 53. The ends of the series-connectedstring of LED dies 27-32 are wire bonded to conductors formed by themetal layer 46. A portion of the solder mask layer 47 on the printedcircuit board 40 is removed to form a landing pad 54 for a bond wire 55that electrically couples the metal layer 46 to the LED die 32, which isdisposed on the top surface 51 of the substrate 26. No electricalconnection is made to any of the LED dies 27-32 disposed on the topsurface 51 of the substrate 26 except through a bond wire 53, 55. In theclaims and this description, terms such as “upper”, “lower”, “top” and“bottom” are used to describe relative orientations between differentparts of the LED device 39, and it is to be understood that the overallstructure being described can actually be oriented in any way inthree-dimensional space. When a first object is referred to as beingdisposed “over”, “above” or “on” a second object, it is to be understoodthat the first object can be directly on the second object, or anintervening object may be present between the first and second objects.

A conformal layer of transparent carrier material 56, such as siliconeor epoxy, covers the substrate 26 and the LED dies 27-32. Particles ofphosphor 57 are suspended in the silicone 56. The phosphor 57 converts aportion of the blue light generated by the LED dies 27-32 into light inthe yellow region of the optical spectrum. The combination of the blueand yellow light is perceived as “white” light by a human observer.

FIG. 4 is a perspective view of the top of the integrated smart lightingmodule formed by encapsulating electronic components over the LEDpackaging device 39. The disk-shaped shaded object in the center of themodule of FIG. 5 is the conformal silicone layer 56 with embeddedphosphor particles. This silicone with the embedded phosphor particlesoverlies the LED dies 27-32. The LED dies are not visible in FIG. 5because they are disposed under the silicone. The highly reflectivealuminum substrate 26 is a disk that is disposed below the siliconelayer 56.

FIG. 5 shows another embodiment of a low-cost LED packaging device 39that provides superior reflectivity and heat conductivity withoutcovering entire surfaces of a luminaire with expensive highly-reflectivealuminum. The device 39 of FIG. 5 is similar to that of FIG. 3 exceptthat a thicker printed circuit board 40 is used to make the luminaire.Because the thickness of the aluminum substrate 26 is typically lessthan one millimeter and the thickness of printed circuit board 40 isoften more than one millimeter, the top surface 51 of the substrate 26will be lower than the upper surface 52 of the printed circuit board 40.Nevertheless, the lower surface 49 of the printed circuit board 40 andthe bottom surface 50 of the substrate 26 will be coplanar after thesubstrate 26 is inserted into the cylindrical hole 48 in the printedcircuit board 40. Because the upper surface 52 of the printed circuitboard 40 is higher than the top surface 51 of the substrate 26 on whichthe LED dies are mounted, an indentation is formed in the LED packagingdevice 39 above the LED dies 27-32. This indentation is filled with alayer of transparent carrier material 56 that covers the substrate 26and the LED dies 27-32. Particles of phosphor 57 are also suspended inthe silicone 56 of the embodiment of FIG. 5. In one embodiment, the hole48 is overfilled such that the high viscosity of the silicone causes thelayer to extend above the upper surface 52 of the printed circuit board40 and to form the curve of a lens.

A larger disk of the aluminum substrate 26 is used in the embodiment ofFIG. 5 than in the embodiment of FIG. 3. It is advantageous to use alarge enough portion of substrate 26 with sufficient distance betweenthe end LEDs 27, 32 and printed circuit board 40 so that the anglebetween the end LEDs 27, 32 and the top of the wall of the cylindricalhole 48 is less that 45 degrees. A lower angle between the end LEDs andthe upper corners of the printed circuit board 40 will decrease theamount of light emitted by the LEDs that is absorbed by the walls of theprinted circuit board.

FIG. 6 is a perspective view of the printed circuit board 40 and thehighly reflective substrate 26 illustrating how small portions of theCOB aluminum substrate 26 are inserted into holes in the printed circuitboard 40 to make the LED packaging device 39. In one embodiment,cylindrical holes 60 are cut into the printed circuit board 40 atlocations where LED dies are desired in the LED luminaire. Disks 61 arecut from the aluminum substrate in a size to fit in the holes 60. Thediameter of each of the disks 61 is slightly smaller than the diameterof each of the holes 60. The spacing between the disks cut from thealuminum substrate 26 is small to reduce the amount of holed substratethat is discarded. In another embodiment, small squares of the COBaluminum substrate 26 are inserted into square holes in the printedcircuit board 40 to make the LED packaging device 39. None of thealuminum substrate 26 remains to be discarded after the substrate is cutinto squares as opposed to disks.

In embodiments in which the top surface 51 of the substrate 26 and theupper surface 52 of the printed circuit board 40 are coplanar in thefinished LED packaging device 39, the LED dies 62 can be mounted ontothe top surface of the aluminum substrate 26 after the portions ofsubstrate are inserted into the holes in the PCB 40. In otherembodiments, LED dies 62 are first mounted directly onto the top surface51 of the top reflective layer 38 of the COB aluminum substrate 26before the disks 61 are cut from the substrate 26. The LED dies 62 aremounted in the pattern used in the LED packaging device 39. For example,the LED device 39 being made in FIG. 6 includes an array of sixty LEDdies 62. FIG. 6 shows an aluminum substrate 26 inside a hole 60 in PCB40 with the top surface 51 of the substrate lower than the upper surface52 of the PCB. Strings of LED dies are electrically connected in seriesby bond wires. For example, ten LED dies across the middle of thecircular array are connected in series such that a drive current canflow from a positive landing pad 54 on PCB 40 through the LED dies to anegative landing pad 58 on PCB 40. The LED dies at the ends of eachstring are connected to the landing pads 54, 58 on PCB 40 by bond wires55.

FIG. 7 shows the LED packaging device 39 used in a luminaire intendedfor outdoor lighting purposes. LED device 39 includes four disks 63-66of the highly reflective aluminum substrate 26 embedded in the PCB 40.The luminaire is a low-profile lighting module 67 that is suitable foruse in street lights, under the canopies of gas stations, on the metalsiding of buildings and in bay lights in warehouses and big box stores.Module 67 has limited space requirements because of its low profile. Forexample, the flat body of module 67 is less than seven millimetersthick. Because module 67 is so thin, it fits in most street lights inthe space that would otherwise be occupied by conventional high-pressuresodium (HPS) bulbs. No solder or screws are used to attach themolded-plastic cover 68 to the printed circuit board 40 on which thecomponents are mounted. The six holes in module 67 shown in FIG. 7 areused to screw the module to a street lamp, metal siding or other heatsink. An array of LED dies 62 is mounted on each of the four disks63-66, and an optical lens 69 is disposed over each LED array. Foradditional details on the low-profile outdoor lighting module 67, seeU.S. patent application Ser. No. 14/229,903 entitled “Low-ProfileOutdoor Lighting Module With Light Emitting Diodes,” filed on Mar. 29,2014, which is incorporated herein by reference.

FIG. 8 is a different perspective view of low-profile lighting module 67of FIG. 7. FIG. 8 also shows that pairs of lenses 69-70 are integrallyattached together by a flat portion 71 of the lens material. The edge ofeach flat portion 71 fits under the lip 72 of openings in cover 68.

FIG. 9A is a longitudinal cross-sectional view of a portion of module 67through two disks 63-64 of LED packaging device 39. The elements of FIG.9A are shown in an exploded view in FIG. 9B for clearer labeling. FIG.9A shows a bolt 73 used to attach module 67 to a heat sink 74. Bolt 73passes through a hole 74 in the molded-plastic cover 68. FIGS. 9A-7Billustrate how the aluminum substrate 26 of the disks 63-64 fits up intothe cylindrical openings 60 in the printed circuit board (PCB) 40 thatforms the base of module 67. The diameter of the opening 60 is somewhatgreater near the lower surface 49 of PCB 40, which forms a lowerindentation 75 in the lower surface 49. The upper portion of the wallsof each disk 63 are ground to decrease the diameter at the top of thedisk 63 and to form a lower lip 76. The lower lip 76 of each disk 63fits up into the lower indentation 75, and the diameter at the top ofthe disk 63 is only slightly smaller than the diameter of each of theopenings 60. Each disk 63-64 is held into an opening 60 by the frictionbetween the walls of the openings 60 and the upper edges of the disk. Inaddition, each COB aluminum substrate 26 is mechanically attached to PCB40 by and adhesive and sealant that lines the lower indentation 75.

There is also an upper indentation 77 located in the upper surface 52 ofPCB 40. The flat portion 71 of the lenses 69-70 fits into upperindentation 77 and is held in place by the lip 72 around openings incover 68. FIG. 9B shows the curved optical portion 78 and the flatportion 71 of lens 69. The peripheral edge of the flat portion 71 ispressed down into upper indentation 77 by the lip 72 around the openingin cover 68. Lens 69 has a hollow dome 79 beneath the curved opticalportion 78.

The molded-plastic cover 68 is attached to the upper surface 52 of PCB40 by a double-sided adhesive sheet 80. Adhesive sheet 80 attaches theinside surface 81 of cover 68 to both the upper surface 52 of PCB 40 andto the flat portion 71 of the lenses 69-70. Because adhesive sheet 80covers both the upper surface 52 of PCB 40 and the flat portion 71 oflenses 69-70, a water-tight seal is created over the groove between thelenses and PCB 40. Thus, moisture is prevented from entering module 67from the light emitting side. Moisture is also prevented from enteringmodule 67 through the lower indentation 75 in PCB 40 by forming aroom-temperature vulcanizing (RTV) rubber seal in the channel betweensubstrate 26 and the walls of the lower indentation 75. The rubber isdispensed into the channel after substrate 26 has been inserted into thelower indentation 75. Thus, module 67 is weatherized and can withstandharsh outdoor usage, such as being bolted to the aluminum siding of abuilding without being protected under a canopy or roof.

When highly reflective substrate 26 is mounted up into lower indentation75, the bottom surface 50 of substrate 26 is substantially coplanar withlower surface 49 of PCB 40. In this manner, the bottom side of module 67can be mounted to the planar surface 82 of heat sink 74 to achieve agood thermal contact. To improve the thermal coupling between module 67and heat sink 74, a thermal interface material 83 can optionally beused. In this case, substrate 26 is thermally coupled through thethermal interface material 83 to heat sink 74. Thermal interfacematerial 83 is placed on upper surface 82 of heat sink 74, and lowersurface 49 of PCB 40 contacts thermal interface material 83. In oneimplementation, thermal interface material 83 is thermal grease, andmodule 67 is attached to heat sink 74 by bolts 74. In anotherimplementation, thermal interface material 83 is thermal glue thatadheres lower surface 49 of PCB 40 to upper surface 82 of heat sink 74.No bolts are required when thermal glue is used. Any small deviations ofsurfaces 27 and 49 from being exactly planar are compensated by thethickness of the thermal interface material.

FIG. 10 shows the bottom side of low-profile lighting module 67 that isattached to heat sink 74. FIG. 10 shows the RTV rubber seal in a channel84 between substrate 26 and the walls of lower indentation 75. Althoughthe bottom rim 85 of molded-plastic cover 68 is not sealed to the sidesof PCB 40, moisture cannot enter between upper surface 52 of PCB 40 andinside surface 81 of cover 68 due to the seal formed by double-sidedadhesive sheet 80. Similarly, moisture is prevented from reaching uppersurface 52 of PCB 40 from round the plastic surrounding the holes 74 bythe seal formed by adhesive sheet 80.

FIG. 11 shows lower surface 49 of PCB 40 before each disk 63-64 of thehighly reflective substrate 26 is inserted up into an openings 60 and alower indentation 75 in the lower surface 49.

FIG. 12 shows a disk 63 of highly reflective substrate 26 before thedisk is inserted into an opening 60. FIG. 12 also shows the LED dies 62that are directly attached to the top surface 51 of the substrate 26 onthe reflective layer 38.

FIG. 13 shows PCB 40 from the top side after the disks 63-64 ofsubstrate 26 have been inserted from the bottom into the openings 60.The landing pads 54, 58 at the upper edges of the openings 60 are formedby exposed portions of metal layer 46. The top surface 51 of each disk63-64 is lower than the surface of PCB 40 at the bottom of upperindentation 77. The indentation formed by the lower top surface 51 ofeach disk 63-64 is filled with silicone 56 containing phosphorparticles. The silicone is poured into the indentation and hardensforming a conformal covering over the LED dies 62.

FIG. 13 also shows a plurality of electronic components, including driveelectronics, are mounted onto PCB 40. The drive electronics areelectrically coupled to the LED dies 62 through the metal layer 46 ofPCB 40 and the landing pads 54, 58. A structure 54 contains electroniccomponents that power and control the LED dies 62. In the embodiment ofFIG. 13, the electronic components in structure 54 can be damaged byexcessive heat. By using a composite substrate with aluminum disksinserted into holes in an FR-4 printed circuit board as opposed to acomplete COB aluminum substrate, the amount of heat that flows from theheat sink back up to the electronic components can be reduced. If thestructure 54 were mounted on an aluminum board that is in contact withthe head sink 74, then the temperature of the electronic componentsmight increase if the LED dies 62 generate such large amounts of heatthat the heat sink 74 cannot dissipate that heat before the temperatureof the heat sink increases. The glass and resin of PCB 40 insulate thestructure 54 from heat that might otherwise be transferred from the LEDdies 62, through the COB aluminum substrate 26, to the heat sink 74 andback up to the structure 54.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A device comprising: a substrate with a topsurface and a bottom surface, wherein the substrate includes aninsulating layer, a reflective layer and a thicker aluminum layer, andwherein the insulating layer and the reflective layer are disposed abovethe aluminum layer; and a printed circuit board having a layer of glassfiber in resin, a metal layer, a lower surface, and an upper surface,wherein the substrate is disposed in a hole in the printed circuitboard, and wherein the lower surface of the printed circuit board andthe bottom surface of the substrate are substantially coplanar.
 2. Thedevice of claim 1, wherein the substrate has a reflectivity of greaterthan 97%.
 3. The device of claim 1, further comprising: a light emittingdiode (LED) die disposed on the top surface of the substrate, whereinthe metal layer is electrically coupled to the LED die through a bondwire.
 4. The device of claim 3, wherein the substrate also includes atop layer of reflective material, and wherein the LED die is mounteddirectly to the top layer.
 5. The device of claim 1, wherein noelectrical connection is made to any LED die disposed on the top surfaceof the substrate except through a bond wire.
 6. The device of claim 1,wherein the top surface of the substrate and the upper surface of theprinted circuit board are coplanar.
 7. The device of claim 1, whereinthe top surface of the substrate is lower than the upper surface of theprinted circuit board.
 8. The device of claim 1, further comprising: alight emitting diode (LED) die disposed on the top surface of thesubstrate; and a layer of silicone that covers the substrate and the LEDdie, wherein particles of phosphor are contained in the layer ofsilicone.
 9. The device of claim 1, further comprising: a light emittingdiode (LED) die disposed on the top surface of the substrate; andelectronic circuitry disposed on the upper surface of the printedcircuit board, wherein the electronic circuitry is used to control lightemitted from the LED die.
 10. The device of claim 1, further comprising:a light emitting diode (LED) die disposed on the top surface of thesubstrate; and drive electronics disposed on the upper surface of theprinted circuit board, wherein the drive electronics receive a highervoltage and supply a lower voltage to the LED die.
 11. A devicecomprising: a light emitting diode (LED) die; a highly reflectivesubstrate with a top surface and a bottom surface, wherein the LED dieis disposed on the top surface of the substrate, wherein the substrateincludes an insulating layer, a reflective layer and a thicker aluminumlayer, and wherein the insulating layer and the reflective layer aredisposed above the aluminum layer; and a printed circuit board having alayer of glass fiber in resin, a metal layer, a lower surface, and anupper surface, wherein the substrate is disposed in a hole in theprinted circuit board, wherein the lower surface of the printed circuitboard and the bottom surface of the substrate are substantiallycoplanar, and wherein the metal layer is electrically coupled to the LEDdie through a bond wire.
 12. The device of claim 11, wherein the topsurface of the substrate is lower than the upper surface of the printedcircuit board.
 13. The device of claim 11, wherein the printed circuitboard has a lower indentation in the lower surface, wherein the lowerindentation has a depth, wherein the substrate has a lower lip with athickness, and wherein the thickness of the lower lip equals the depthof the lower indentation.
 14. The device of claim 11, furthercomprising: a cover of molded plastic with an inside surface, wherein adouble-sided adhesive sheet is disposed under the inside surface of thecover and over the upper surface of the printed circuit board.
 15. Thedevice of claim 14, further comprising: drive electronics disposedbetween the upper surface of the printed circuit board and the insidesurface of the cover.
 16. The device of claim 15, wherein the driveelectronics receive a higher voltage and supply a lower voltage to theLED die.
 17. The device of claim 11, further comprising: a heat sinkwith an upper surface; and a thermal interface material, wherein thebottom surface of the substrate contacts the thermal interface material,and wherein the upper surface of the heat sink contacts the thermalinterface material.
 18. The device of claim 11, further comprising: adouble-sided adhesive sheet; a cover of molded plastic with an insidesurface, wherein the adhesive sheet is disposed under the inside surfaceof the cover and over the upper surface of the printed circuit board;and a lens with a planar lower surface and a flat portion, wherein theadhesive sheet is disposed under the inside surface of the cover andover both the upper surface of the printed circuit board and the flatportion of the lens.
 19. A device comprising: a light emitting diode(LED) die; a printed circuit board having a layer of woven glass fabricin epoxy resin, a metal foil conductor, a lower surface, and an uppersurface, wherein a cylindrical hole is disposed in the printed circuitboard; and a means for reflecting light emitted by the LED die, whereinthe means includes an insulating layer and a reflective layer disposedabove a thicker aluminum substrate, wherein the means is disposed in thecylindrical hole, wherein the LED die is mounted directly to the topsurface of the means, wherein the lower surface of the printed circuitboard is substantially coplanar with a bottom surface of the means, andwherein the conductor is directly connected to the LED die by a bondwire.
 20. The device of claim 19, wherein no electrical connection ismade to any LED die disposed on the top surface of the means exceptthrough a bond wire.
 21. The device of claim 19, further comprising: alayer of silicone that covers the means and the LED die, whereinparticles of phosphor are contained in the layer of silicone.
 22. Thedevice of claim 21, wherein the layer of silicone extends above theupper surface of the printed circuit board.